Once filled, containers are immediately capped, at a capping unit, with caps supplied by a cap feeding unit.
In an ordinary cap feeding unit, caps are supplied from a hopper into a cap feeding line where caps are moved in at least one row towards the capping unit. As caps are initially stored in a non-sterile environment (such as a hopper), they are generally sterilized before they reach the capping unit.
More precisely, caps are generally moved by a cap transfer unit, along a transfer path, through a sterile chamber where sterilization is realized, e.g. by spraying hot hydrogen peroxide, in order to subsequently close the containers which have been filled in aseptic conditions. One may refer to US patent application No. US 2007/0006550 (SIG TECHNOLOGY) for further details regarding cap sterilization.
Several technologies are ordinarily used to move the caps along their path, depending upon the configuration of the feeding lines and the operations the caps are undergoing. For example, cap supply from the hopper may be achieved by the sole gravity, to an inclined (or vertical) feeding line. In other portions of their path, the caps may be moved by a stream of pulsed air, provided by air nozzles located in the vicinity of the path. It is critical to ensure smooth and quick movement of the caps, since, in the end, the cap supply rate must be equal to the predetermined capping rate, which in turn is equal to the container filling rate. Nowadays such rates can reach up to several tens of thousands units per hour.
Cap transfer through the sterilization chamber is a peculiar operation in cap handling, for submission of the caps to the sterilization agent must take a predetermined time, which must be long enough to achieve sterilization, and yet short enough to avoid cap damage since hot hydrogen peroxide may cause surface attack.
This is why, in the sterilization chamber the moving speed of the caps is generally controlled, e.g. by means of a transfer wheel located in a loading area of the cap transfer line, the rotational speed of which is set to a predetermined value. It is also preferable to arrange horizontally the cap transfer line, in order to avoid uncontrolled displacement of the caps during the sterilization process. Furthermore, since the environment in the sterilization chamber must be kept sterile, it is not allowed to use air nozzles to force the caps along the transfer line.
Such a design may lead to a major difficulty. When caps are missing upstream the transfer wheel, e.g. because of an upstream cap jam or emptiness of the hopper, the caps standing along the transfer path in the sterilization chamber are stopped, thereby leading to cap damage.